1. Technical Field
Embodiments described herein relate to an airbag apparatus mounted on a vehicle such as an automobile, and to a method for sewing a tether for the airbag or airbag apparatus. In particular, the embodiments described herein relate to an airbag apparatus and a tether sewing method for sewing a tether for restricting an airbag shape.
2. Related Art
Vehicles such as automobiles are usually equipped with airbag apparatuses for inflating and deploying airbags inside the vehicles, for example, at the time of collision or abrupt deceleration to absorb impact exerted on occupants. Various types of such airbag apparatuses have been developed and adopted. Among them are a driver-side airbag apparatus inserted into a steering wheel, a passenger-side airbag apparatus inserted into an instrument panel, a side airbag apparatus inserted into a vehicle lateral portion or a seat, a curtain airbag apparatus inserted into a door upper portion, and a knee airbag apparatus located at a position corresponding to an occupant's knee.
These airbag apparatuses each usually have: an airbag that is folded up in normal times and is inflated and deployed in an emergency; and an inflator for supplying gas to the airbag. In particular, in the case of the passenger-side airbag apparatus, an airbag inflation space is large, and people of various body types such as a child, an adult female and an adult male may sit in a passenger seat; therefore, it is required that consideration be made to bring factors such as an airbag volume, an inflation/deployment speed, an airbag internal pressure and an impact absorbing ability into balance. In terms of such requirements, a tether for restricting an airbag shape (which may also be referred to as a “strap”, “belt part”, “band-like body” or “band-like string”, for example) may be placed inside the airbag (see JP-A-5-116575 and JP-A-7-304411, for example).
JP-A-5-116575 describes the following points. Since an airbag is primarily largely extended in an ejection direction in which gas is ejected from an inflator, i.e., in a direction toward an occupant, during an initial airbag deployment period, there arises a problem that the inflation of the airbag in vertical and lateral directions is delayed; hence, with the aim of limiting the extension of the airbag in the gas ejection direction, a strap for restricting the extension of the airbag is often provided so that the strap runs between a position in the vicinity of an inward top portion of the airbag and a position in the vicinity of an inward base portion of the airbag.
Further, JP-A-5-116575 discloses a method for fabricating a vehicle airbag in which band-like bodies are provided by integrally extending part of respective reinforcement fabrics attached to positions in the vicinities of the inner top portion and inner base portion of the airbag that is in the form of an deployed shape, and straps for restricting the deployed shape of the airbag are formed by sewing ends of the band-like bodies of the reinforcement fabrics opposed to each other. The vehicle airbag fabricating method is characterized by the following features. Flaps having set holes are formed at respective tip portions of the band-like bodies by being protruded from the tip portions to both sides; on the other hand, positioning pins are provided at a mating surface of a pair of plate-like bodies, having sewing through holes, so that the positioning pins correspond to the set holes of the band-like bodies superposed for sewing, thus providing a sewing jig. The positioning pins of the jig are inserted through the set holes of the band-like bodies which are to be sewn to each other, and then the plate-like bodies of the jig are closed to sew the ends of the band-like bodies through the sewing through holes.
JP-A-7-304411 discloses a method for fabricating an airbag main body of an airbag apparatus in which the airbag main body swells out at the time of operation of a gas generator, the airbag main body is formed by sewing edges of a front-side base fabric and a rear-side base fabric having a gas inlet, a hanging belt is sewn between the front-side base fabric and the rear-side base fabric, and a belt part tip of the hanging belt is sewn to belt catches sewn to the airbag main body. The airbag main body fabricating method is characterized by the following features. The belt part tip of the hanging belt is provided, at its positions closer to the tip than a position where a sewn portion is to be formed, with pin holes for insertion of positioning pins, the belt catches opposed to these pin holes are provided with pin holes for insertion of the positioning pins, the positioning pins formed at a sewing machine table are fitted into the pin holes of the belt catches and the pin holes of the belt part tip to determine positioning, and then the sewn portion of the belt part tip of the hanging belt is formed.
Actually, in sewing a tether such as one described above to a base fabric of an airbag, accurate fixation of the tether is enabled but pin holes remain after the sewing when the tether is fixed to the airbag with the use of positioning pins, thus making it necessary to provide a step of closing the pin holes. Therefore, for example, the airbag base fabric is deployed on a plane on a bench, an outer peripheral portion of the airbag is fixed on the bench via positioning pins, a sewing position of the tether is pointed out by a laser pointer or the like, and then the sewing of the tether is carried out. However, such a sewing method causes a problem that facilities are increased in size because the entire airbag has to be deployed on a plane, and a problem that a wrinkle is likely to occur in the airbag base fabric because a fixed portion of the airbag and a sewn portion of the tether are located away from each other.
Furthermore, in sewing ends of the tethers (band-like bodies) for restricting an airbag shape in the vehicle airbag fabricating method according to Patent Document 1 described above, the flaps having set holes are formed in the tethers (band-like bodies) and the positioning pins are inserted through the set holes, thereby enabling accurate positioning. However, no particular reference is made to sewing of the tethers (band-like bodies) to positions in the vicinity of the inner top portion of the airbag, and therefore, problems similar to those in the conventional sewing method might occur.
Moreover, in the airbag main body fabricating method according to Patent Document 2 described above, the tether (hanging belt) is sewn to the belt catches, and the positioning pins are inserted through the pin holes formed in the tether and the belt catches, thereby enabling accurate positioning. However, no particular reference is made to sewing of the airbag base fabric to the belt catches, and therefore, problems similar to those in the conventional sewing method might occur.